26S 
PROCEEDINGS OF THE PERTHSHIRE SOCIETY OF NATURAE SCIENCE. 
between the Arctic and Antarctic circles, is close upon 8000 
geographical miles. 
The greatest depth found in the recent soundings of the 
Challenger , which waB that of a limited depression about 
85 miles north of St Thomas in the West Indies, is 3857 
fathoms, or about 4‘4 miles. Except in the neighbourhood 
of its coast lines, and in certain shallower area3, the floor 
of the basin in its widest part seems to be at a depth of 
2000 to 3000 fathoms. The central portion of the principal 
basin of the North Atlantic, however, is occupied by a 
plateau of irregular shape, of which a considerable part 
lies at a less depth than 2000 fathoms. 
The Pacific Ocean is the largest expanse of water in the 
world, covering fully a third of its surface, almost one-half 
of the water surface. It extends through 133 degrees of 
latitude, or, in other words, it measures 9180 miles from 
north to south. Its area has been estimated at 67,810,000 
square miles. The Pacific is considerably more than all 
the land surface. The weight of the earth, assuming that 
its mean density was 5'6 times that of pure water, would 
be, in round numbers, 6000 trillions of tons. The coast 
line of the Pacific and Indian Oceans, taken together, 
amounts to only 47,000 miles; whilst that of the Atlantic 
alone measures 55,000—the smaller ocean making up for 
its less extent by its numerous inland seas of smaller size. 
The drainage area of the Pacific is estimated at 8,660,000 
square miles; while that of the Atlantic amounts to more 
than 19,000,000. The chief reason for the disparity is that 
only 500,000 of square miles of the American Continent 
drain into the Pacific — the remaining 6,500,000 being 
connected with the Atlantic river systems, and it is 
estimated that only l-7th of the area of the Asiatic 
Continent drains into the Pacific. The Asiatic division 
of the Pacific river system is very much more extensive 
than that of the American, and includes many streams of 
great size and commercial importance. In the north, the 
Amoor is more than 2000 miles long, and it has many 
tributaries. Its drainage is calculated at 90,000square miles. 
The Hoang-Ho has a length of 2600 miles; and the Yang- 
tse-Kiang measures 3200 miles, from its source to the sea. 
Of the rivers which discharge their waters into the 
Atlantic, the Mississippi alone discharges a greater 
quantity of water than the eight principal rivers of Asia. 
The Mississippi, with its branches, affords a greater amount 
of inland navigation than all the streams great and small 
which irrigate Europe ; and the Plata, in that respect, 
claims a superiority over the collective rivers of Africa. 
But the American rivers not only surpass those of the Old 
World in length and volume of water—they are so placed 
as to penetrate everywhere to the heart of the Continents 
The estuaries of all the great American rivers open to the 
eastward, and it should be observed that the position of 
the great rivers of the New World is but one example of 
a physical arrangement which is common to the whole 
globe; for it is remarkable that in the Old World as well 
as in the New, no river of the first class flows to the west¬ 
ward. The depth of the Indian Ocean averages about 2500 
fathoms, increasing to 3000 fathoms, or 3’4 miles. 
January 21st, 1886. 
CONVERSAZIONE. 
A conversazione of members and their friends was held 
in the Society’s Rooms. Notwithstanding the wintry 
weather, there was a fair attendance. The chief attrac¬ 
tion was the Museum, where there was abundant evidence 
that during the past year members in charge of the various 
departments had not been idle. Every available wall and 
floor space was occupied by cases, the majority of which 
were quite filled. As usual, the collection of Perthshire 
birds, and also that of birds’ nests and eggs, were greatly 
admired. 
In the Lecture-Room, the cases of Perthshire insects 
were displayed round the wall, while in the centre a num¬ 
ber of microscopes were exhibited by various members, 
under the general charge of Mr John Campbell. In these 
were shown microscopic objects of interest in all depart- 
partments of natural history. Perhaps the most admired 
were a series of sections of the local crystalline rocks, 
shown by aid of the polariscope. In this room also Mr R, 
Brown, C.E., R.N., exhibited a large collection of Parisian 
views by the aid of the graphiscope. In the Library, 
Messrs R. D. and A. E. Pullar exhibited a most interest¬ 
ing series of photographic transparencies through the 
megalethoscope. 
